(a) Field of the Invention
The present invention relates to a resin intake manifold for feeding air to intake ports of a multicylinder engine.
(b) Description of Related Art
As disclosed by Japanese Unexamined Patent Publications Nos. 2002-235619 (Patent Literature 1) and 2002-70670 (Patent Literature 2), there has been known a resin intake manifold including a plurality of intake paths connected to individual intake ports of an inline multicylinder engine. If a resin is used to form the intake manifold as disclosed by these patent literatures, the shape of the intake manifold can be designed with a high degree of freedom. Therefore, a throttle body mounting part for mounting a throttle body having a throttle valve and a surge tank can be integrated with the intake paths.
The resin intake manifold of Patent Literature 1 is formed of a combination of four manifold components. One of the manifold components to be mounted to the engine is configured to extend downward with inclination from the engine to the direction away from the engine. On the top of the manifold component attached to the engine, another manifold component which constitutes part of the intake paths is welded and the throttle body mounting part is integrated with the welded manifold component. Further, the other two manifold components which constitute the surge tank and part of the intake paths are welded to the bottom of the manifold component attached to the engine.
On the other hand, the resin intake manifold of Patent Literature 2 is formed of a combination of three manifold components which are separated in the vertical direction. Among them, the top manifold component is attached to the engine and integrated with the throttle body mounting part. The other two manifold components are welded below the top manifold component.
Since the intake manifold is fixed to the engine, the vibration of the engine is directly transmitted to every part of the intake manifold. Therefore, if the intake manifold is formed by welding a plurality of resin manifold components together as disclosed by Patent Literature 1, they must be welded firmly enough not to be separated from each other. However, according to Patent Literatures 1 and 2, the bottom side of the manifold component attached to the engine and the top side of another manifold component are welded together. Therefore, the weight of the lower manifold component is exerted downward on the welding interface between the manifold component attached to the engine and the lower manifold component, i.e., force is applied in the direction in which the manifold components are separated. Thus, there is a difficulty in maintaining a welding strength of a satisfactory degree.
Further, since the intake manifold of Patent Literature 1 is formed of four manifold components, the number of steps of welding the manifold components increases, causing a problem in mass productivity.